Mere hours after stumbling upon the radioactive hot spots, they also found a slow leak from a pipe connecting two tanks holding contaminated water which they sealed with absorption material and tape. Radiation from the puddle below it was measured at 230 millisieverts per hour, Tepco said.

The high readings raise fresh concerns over Tepco’s handling of the decommissioning efforts of the embattled nuclear facility.

Just last month, Tepco revealed that 300 tons of highly contaminated water had disappeared from a huge tank, sparking fears that the toxic water may have leaked into the ocean or seeped into the ground.

The International Atomic Energy Agency criticized Japan for the rating, which denotes a serious incident, and said it was confusing the public.

Prime Minister Shinzo Abe vowed that his government would take a more central role in tackling the crisis amid domestic and international pressure on Tepco to seek outside help.

“The accident in Fukushima cannot be left entirely to Tokyo Electric Power. There is a need for the government to play a role with a sense of urgency, including taking measures to deal with the waste water,” Abe said.